The invention relates to an apparatus for removing water from blood in an extracorporeal circuit, comprising a filter which is connected on the blood inlet and outlet side via a supply line and an offtake line to at least one blood connection, the supply line having a blood pump and a clamp disposed upstream and downstream of the blood pump and the offtake line having a further clamp and a throttle means.
In the field of intensive medicine high-caloric nutrition frequently leads to hyperhydration of patients and thus to a drop in blood pressure which leads to failure in the filtration performance of the kidneys. To dehydrate the latter it is therefore possible to use the already known usual apparatuses such as hemofiltration machines or volume-controlled dialysis machines which generally are employed for pure dialysis in which apart from the withdrawal of water a cleaning of the blood from metabolism products takes place. Due to this specific use these known machines are tailored to this specific purpose and are made relatively complicated so that it is practically impossible for untrained personnel to Examples of such aforementioned dialysis apparatuses are the known single-needle dialyzers as disclosed for example in U.S. Pat. Nos. 3,811,800, 3,791,767 or DE-OS No. 2,455,917. With the aid of such apparatuses blood is intermittently pumped around a closed circuit and with the aid of the blood pump an excess pressure is produced in the closed circuit which effects the ultrafiltration of plasma water in the hemofilter.
Accordingly, in medicine arteriovenous hemofiltration was found to be a considerable simplification because it does not require any control unit. In this method, both an arterial and a venous access is made surgically and therebetween an extra corporeal circulation is established which includes a hemofilter. With a closed cycle the blood flow rate depends on the flow resistance of the extracorporeal system and the arteriovenous pressure difference whilst the filtration performance depends on the filtration properties of the filter and the venous pressure. The system is constructed so that the filtrate can flow into a collection bag or vessel and from time to time the amount collected measured and checked.
Although it is simple, this system has some serious disadvantages.
Firstly, the extracorporeal circulation is not monitored in any way. Since an arterial connection is present there is therefore an acute danger of loss of blood into the surroundings if a defect occurs in the system or a connection becomes detached.
This can lead to the patient bleeding to death within a few minutes if the extracorporeal cycle is not closed again in good time.
Furthermore, the filtration performance, apart from the choice of the hemofilter and hose material used, cannot be controlled and monitored. This basic disadvantage leads to the filtration performance being low when the hyperhydration is high and the blood pressure has dropped and increasing again only with increasing dehydration and increasing blood pressure. Accordingly, a hyperhydrated patient can only be brought slowly out of a shock due to hyperhydration but fall all the more rapidly into a state of shock induced by excessive dehydration. Thus, in this respect the filtration performance in conventional arteriovenous hemofiltration behaves exactly oppositely to the desired behaviour.